[tip:core/urgent] futexes: Fix infinite loop in get_futex_key() on huge page

tip-bot for Sonny Rao
2009-07-11T08:22:51Z

Commit-ID: 7c8fa4f04ab956076605422d5ed37410893a8a73
Gitweb: http://git.kernel.org/tip/7c8fa4f04ab956076605422d5ed37410893a8a73
Author: Sonny Rao <sonnyrao@us.ibm.com>
AuthorDate: Fri, 10 Jul 2009 18:13:13 -0500
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Sat, 11 Jul 2009 10:18:45 +0200

futexes: Fix infinite loop in get_futex_key() on huge page

get_futex_key() can infinitely loop if it is called on a
virtual address that is within a huge page but not aligned to
the beginning of that page. The call to get_user_pages_fast
will return the struct page for a sub-page within the huge page
and the check for page->mapping will always fail.

The fix is to call compound_head on the page before checking
that it's mapped.

Signed-off-by: Sonny Rao <sonnyrao@us.ibm.com>
Cc: stable@kernel.org
Cc: anton@samba.org
Cc: rajamony@us.ibm.com
Cc: speight@us.ibm.com
Cc: mstephen@us.ibm.com
Cc: grimm@us.ibm.com
Cc: mikey@ozlabs.au.ibm.com
LKML-Reference: <20090710231313.GA23572@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
kernel/futex.c | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 794c862..0672ff8 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -247,6 +247,7 @@ again: